96 PCB007 MAGAZINE I JULY 2024
and signals were placed on the inner layers.
Figure 1
4
shows the new power-signal routing
architecture, which was called power mesh to
differentiate it from IMPS.
Electrical Model
e original Lynx board was not controlled
impedance, but additional PCB designs that
used power mesh were. e consensus is that
power mesh is an offset coplanar stripline.
Figure 9 shows the cross-section and stack-up
for the PMA.
e crosstalk model indicates that the power
mesh architecture creates a naturally low cross-
talk condition. Each signal trace of X-width
is approximately 3X or 4X distance from the
next signal, depending on the power trace
width. is creates horizontal crosstalk of less
than 2%. e vertical crosstalk is extremely
low. From 15 mV/V for thin cores (0.012") to
2.6 mV/V for a thick core (0.051").
Wiring Model
In 1994, StorageTek, an OEM in Colorado,
conducted performance benchmarking with
microvia designs and fabrication. e successes
of that program contributed to its continued
use of microvias. In 1998, it became apparent
that they required some wiring model to indi-
cate that a microvia structure was required. In
performing that model development, a power
mesh benchmark was designed for one of the
microvia boards. Figure 5 in Tech Talk #28
shows the two inner layers of the four-layer
power mesh structure and two of the six inner
layers from the original eight-layer through-
hole design. e wiring density model for the
power mesh architecture is:
Power mesh = 17 to 40 signal inches per
square inch per layer*
• Calculate the statistical wiring density
using Coors, Anderson & Seward
4
• Calculate the Manhattan wiring density
using Wd = 0.0068(X)^2 – 0.1644(X) +
35.1, where X is the Coors statistical
wiring density
• Calculate the routability index for power
mesh
• Calculate the layout efficiency using L.E.
(%) = 4.0642(RI)^ – 1.189, where RI is
the routability index
* Dependent on trace width and spacings
Summary
e new microvia topologies of swing vias,
VeCS, IMPS, and power mesh have demon-
strated that applications to simplifying complex
multilayer, PBGAs, and MCMs to UHDI are
available. VeCS can reduce process costs; IMPS
can reduce the structure to a two-metal inter-
connect, while power mesh uses a four-layer,
reinforced laminate structure. ese results
show that these topologies have the capacity of
positively impacting how electronic products
are packaged and interconnected. PCB007
References
1. Chapter 3: Swing Vias, The HDI Handbook, by
Happy Holden, I-Connect007.
2. Happy's Tech Talk #1: Vertical Conductive
Structures (VeCS), by Happy Holden, PCB007 Mag-
azine, October. 2021.
3. I have written nine articles on VeCS for PBC007
Magazine.
4. Happy's TechTalk #27: Integrated Mesh Power
System (IMPS) for PCBs, by Happy Holden, PCB007
Magazine, March 2024.
5. Happy's Tech Talk #28: The Power Mesh Archi-
tecture for PCBs, by Happy Holden, PCB007 Maga-
zine, April 2024.
Happy Holden has worked in
printed circuit technology since
1970 with Hewlett-Packard,
NanYa Westwood, Merix, Fox-
conn, and Gentex. He is cur-
rently a contributing technical
editor with I-Connect007, and
the author of Automation and Advanced Proce-
dures in PCB Fabrication, and 24 Essential Skills
for Engineers. To read past columns, click here.
